this post was submitted on 02 Oct 2024
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I see a future where an EV will have two batteries each with different chemistries. An example would be to have LFP for the "main" battery which can take a beating but is less dense, and an additional NMC battery which gets used far less frequently, but is available for the less frequent long distance needs. This could also mean that when the LFP is dead from use, it can be replaced independent of the NMC which will have had a fraction of the charge/discharge cycles.
If you meant for a single car, that might be a bit lofty, but for options available it makes sense (ie different trim packages for single model sort of thing).
I see it breaking down as follows: Grocery-getter for an old couple won't need much capacity. Just enough to get around town over the course of a day of needed and can plug in and fully charge overnight from a wall outlet. The other would be a battery capable of larger distances but needs a little bigger outlet to charge between stops of a long trip.
What difficulty do you see with this concept in a single car? This technically exists already as there are multiple charge controllers and BMS systems in EVs shipping today, they are just managing different modules of identical chemistries in the single car.
Not so much difficulty but practicality. I would see it being similar to having 2 gas tanks in a car where one is for a high octane fuel and the other for a low performance fuel like ethanol.
And these exist completely separate to EVs. They're called bi-fuel vehichles.
"How Do Bi-fuel Propane Vehicles Work? Bi-fuel propane vehicles typically use a spark-ignited internal combustion engine. A bi-fuel propane vehicle can use either gasoline or propane in the same internal combustion engine. Both fuels are stored on board and the driver can switch between the fuels. The vehicle is equipped with fuel tanks, fuel injection systems, and fuel lines for both fuels" source
They aren't common in the USA because of they way emissions laws were written which made it uneconomical in many cases for auto makers.
There isn't the same challenge in EVs, especially where we're talking the "fuel" is just electricity which is common to both chemistry batteries. I see no challenge for EVs.
I was entirely unaware of this type of vehicle so my initial comment was made without considering them. If there is a market case for such a vehicle, then they would likely fall into that same category.
This has me insanely curious as to where these are common and what are their emissions laws. Time for a trip down a rabbit hole.
I looked into getting one of these or converting my own car to be gasoline and methane about 15 or 20 years ago. Here's what I learned during that time. I don't know if any of this legal information is out-of-date now. During the really early days of bi-fuel cars, homebrew cars were very bad polluters because they'd skip the emmisions systems altogether. This changed when the law was put in place requiring catalytic converters on all cars that burned gasoline.
The challenge then with a bi-fuel car was you needed to build an emissions system that is compatible with two entire different fuels, with different combustion products. That is not a small challenge. This is fine for the gasoline side, however, there isn't really a catalytic converter for methane because the exhaust gasses were actually cleaner than exhaust from a gasoline engine even after passing through the catalytic converter. So there was no market to create a cheap methane catalytic converter because it would have been nearly useless. The law didn't care though and there was no exception for bi-fuel cars.
There WAS an exception in the law for methane only cars, which is why you could actually buy methane (CNG) cars from major manufacturers like the Honda Civic GX:
source
If you wanted to buy a used one of these, you can still find them and fill your CNG tank from your home's natural gas line.
Autotrader link showing Honda Civic GX for sale